Sizing broach



Patented Dec. 15, 1942 SIZING BROACH Wilrese J. Phaneuf, Hudson, Mass, assignor to The Lapointe Machine Tool Company, Hudson, Mass., a corporation of Maine Application February 21, 1941, Serial No. 380,055

4 Claims.

This invention relates to a breach for sizing the bore or inside diameter of a spirally grooved hole, such as the barrel of a pistol, rifle or other firearm.

It is the general object of my invention to provide a sizing breach for previously grooved work which has means to produce a lead or twist of the breach relative to the work during the sizing operation, corresponding to the lead or twist of the previously formed grooves.

To the accomplishment of this object, 1 provide one or more pilot sections in my improved breach in addition to the breaching sections, and each of these pilot sections is provided with spiral ribs or projections fitting the grooves already formed in the work and of the same lead or twist.

My invention further relates to arrangements and combinations of parts which will be hereinafter described and more particularly pointed out in the appended claims.

A preferred form of the invention is shown in the drawing, in which Fig. 1 is a side elevation of my improved breach, partially broken away;

Fig. 2 is a transverse sectional view, taken along any one of the lines 2-2 in Fig. 1;

Fig. 3 is a transverse sectional view, taken along the line 33 in Fig. 1; and

Fig. 4 is a sectional View of a piece of work which illustrates the intended use of my invention.

Referring to Fig. 1, my improved breach comprises a shank portion III by which the breach is pulled through the work, a pilot section II, a breaching section l2 having a series of breaching members I3, a second pilot section M, a sec-- ond breaching section [5 having additional breaching members I6, a third pilot section I1, and a rear end portion 18.

The pilot sections H, M and I! are substantially identical, except that the section I I may be of reduced axial length. Each pilot section comprises a series of spiral ribs 20 adapted to fit the spiral grooves 2| (Fig. 4) previously formed in a firearm barrel B or other similarpiece of work to be sized. A circumferential groove or recess 22 may be formed at the middle of each pilot section for clearance purposes.

The breaching members l3 and 5 are each of full circular configuration and they increase slightly but progressively in diameter through the first cutting section [2 and also, if desired, through the first part of the second cutting section I5.

The remaining breaching members IS in the second breaching section 15 will be of the full diameter of the desired bore and are efiective to accurately size and smoothly finish the inner surface or bore of the barrel.

In using my improved breach, the work is preferably mounted in a rotatable work holder having anti-friction thrust bearings, so that the work may be free to turn as the breach is drawn through the grooved or rifled opening therein.

Successive pilot sections II, M and I1 are provided, so that some part of one or more pilot sections will always be in the grooves of the work during a breaching operation.

With this construction, the breaching members l3 and I6 move through the work with the same relative lead or'twist as the tool which produced the original grooves 2!. The bore is sized by removal of successive slight increments of stock between the grooves 2|, as indicated at 22 in Fig. 4. The breach is centered in the here by the spiral ribs on the pilot sections.

In drawing a breach or other cutting tool through a piece of work, it is unavoidable that slight tool marks will be produced in the finished surface. But with my improved breach all such marks in the inner surface or bore will be parallel to the lead or twist of the grooves 2|, rather than parallel to the axis of the work.

Consequently, when a bullet or other projectile is fired through a barrel, as B, any tool marks appearing on the inner surface will be parallel to the twisting forward movement of the projectile, so that said marks will not retard the travel of the projectile but will have a tendency to additionally guide the projectile in its desired twisting or rotating forward movement,

Having thus described my invention and the advantages thereof, I do not wish to be limited to the details herein disclosed, otherwise than as set forth in the claims, but what I claim is:

1. A breach for reaming and sizing the inner surface of a spirally grooved hole which comprises a pilot section having spiral ribs fitting the grooves in said hole and of corresponding twist, and a plurality of successively operative circular breaching members having continuous peripheral cutting edges and progressively increasing in diameter and effective to size and smooth the inner cylindrical surface of said hole, said circular breaching members receiving a twisting movement from said pilot section as the llelrcliach is drawn through the previously grooved 2. A breach for reaming and sizing the inner surface of a spirally grooved hole which comprises spaced pilot sections each having spiral ribs fitting the grooves in said hole and of corresponding twist, and a plurality of successively operative circular broaching members having continuous peripheral cutting edges and progressively increasing in diameter and interposed between said pilot sections, said circular broaching member being effective to size and smooth the inner cylindrical surface of said hole and receiving a twisting movement from said pilot sections as the broaoh is drawn through the previously grooved hole.

3. The combination in areaming and sizing breach as set forth in claim 2,'in which-a series broaching section and maintains the relative twist of the broach during completion of the sizing operation.

WILROSE J. PHANEUF. 

